1. Field of the Invention:
This invention relates to an image shake suppressing device which is equipped with a camera or the like and arranged to detect vibrations of a relatively low frequency and to suppress a shake of an image on the basis of the detected vibrations as information to be used for preventing the image shake and more particularly to an improvement on a correcting optical mechanism to be used for the device.
2. Description of the Related Art:
The prior art relative to this invention is described by way of example below on the assumption that the image shake suppressing device is applied to a camera.
The cameras of today are arranged to automatically carry out all the important shooting actions such as determining an exposure, focus adjustment, etc., in such a way as to minimize the possibility of a faulty photographing operation by a person unfamiliar with the camera. However, it is hardly possible to automatically prevent a photographic shooting failure resulting from a camera shake. Therefore, research has recently begun for a camera that is capable of preventing a shooting failure caused by the camera shake.
Generally, in the event of a camera shake, the camera vibrates at a frequency between 1 Hz and 12 Hz. In order that a picture is taken without any image shake despite of the camera shake, it is necessary to detect the vibrations of the camera and to displace a correcting lens according to a vibration value detected. Therefore, to attain this purpose, the vibration of the camera must be accurately detected and then an optical axis must be corrected for any change thereof that results from the camera shake.
Theoretically, it is possible to prevent a camera from vibrating by providing it with a vibration sensor which is arranged to detect an angular acceleration and an angular velocity; a camera shake detection system which is arranged to produce an angular displacement value obtained by electrically or mechanically integrating a signal produced from the vibration sensor; and a correcting optical mechanism which is arranged to decenter the optical axis.
FIG. 24 of the accompanying drawings shows by way of example the prior art arrangement of the correcting optical mechanism, which is of a parallel-link type and is disclosed in U.S. Pat. No. 4,864,339. Referring to FIG. 24, a stationary frame 23 which carries a correcting lens 22 for suppressing an image shake is mounted on a first holding frame 26 through a pitch parallel link 235p. This arrangement enables the stationary frame 23 to be movable relative to the first holding frame 26 in the pitch direction 21p. The first holding frame 26 is mounted on a second holding frame 219 through a yaw parallel link 235y in such a way as to be movable relative to the second holding frame 219 in the yaw direction 21y. Further, since the second holding frame 219 is secured to a lens barrel which is not shown, the correcting lens 22 is movable in the pitch and yaw directions 21p and 21y relative to the lens barrel. Coreless motors 230p and 230y are mounted on the lens barrel through base plates 230p and 230y. On the coreless motors 231p and 231y are mounted cams 232p and 232y (not shown) which are arranged to be in contact with the stationary frame 23 and the first holding frame 26 respectively. An intermediate plate 233 and a ball bearing 234 are arranged to remove any friction from between the cam 232p and the stationary frame 23.
When the cams 232p and 232y are lifted by the rotation of the coreless motors 231p and 231y, the stationary frame 23 and the first holding frame 26 are pushed by these cams. This causes the correcting lens 22 to be driven in the pitch and yaw directions 21p and 21y.
Further, springs 236p and 236y are mounted on the parts of the frames 23 and 26 located opposite to the cams 232p and 232y. Since the cams 232p and 232y are constantly pushed by these springs, the correcting lens 22 is driven in the reverse direction when the lift height of the cams 232p and 232y is decreased by the reverse rotation of the coreless motors 231p and 231y.
However, the correcting optical mechanism which is arranged in the above-stated manner necessitates use of the intermediate plate 233 and the ball bearing 234 as the friction removing means to be arranged between the cam 232p and the stationary frame 23 and between the cam 232y and the first holding frame 26 respectively. The ball bearing 234 is not only expensive but also requires a large space. Besides, the arrangement necessitates removal of play between the cams 232p and 232y and the frames 23 and 26 by the forces of the springs 236p and 236y. Therefore, the conventional device is incapable of following any movement exceeding the resonance frequency of the springs. This problem may be solved by increasing the force of the springs. However, the power of the coreless motors 231p and 231y is limited. Besides, the spring force cannot be sufficiently increased in respect of consumption of electric energy. It has been thus impossible to cause the correcting optical mechanism to follow the shake of the camera at a sufficiently high speed.